The invention relates to a method of impregnating decorative or patterned papers used for the production of highly wear-resistant laminate flooring materials, in which the decorative paper is first moistened and impregnated with an amino resin as well as the resin content being regulated in this step.
It is known (patent of Graudenz et al.), to produce highly wear-resistant decorative paper impregnates for laminate flooring materials. In this known process, after the actual impregnation, there is applied to the patterned paper a mass in which the particulate corundum is held relatively stable by special viscosity-increasing substances in a dispersion forming the mass.
In this arrangement the mass is applied by means of spreading rollers still in the wet phase directly after the impregnation or alternatively in an intermediate drying stage.
In this known technology making use of spreading rollers the corundum-containing mass is present in reservoir vessels in which there are formed dead zones, in which there is little movement of the mass. Accordingly the corundum particles settle out, which has the consequence of a lack of homogeneity in the application of the corundum to the paper and thereby substantial variations in the wear resistance values of the resulting laminate flooring materials.
For this reason hitherto viscosity-increasing substances, as a rule cellulose derivatives, have been added to the mass containing the corundum mixture. Furthermore the corundum should be relatively fine, as the lighter or finer corundum particles are less rapidly precipitated. However the introduction of cellulose derivatives leads to an optical dulling of the surface of the laminate flooring materials produced.
The finer the particle size of the corundum, the more must be the proportion of it applied to the decorative paper in order to achieve sufficient wear resistance. Also this results in a dulling of the surface of the materials produced.
The invention is based on solving the problem of avoiding the above-mentioned drawbacks of the known manufacture of highly wear-resistant laminate flooring materials and to be able to produce highly wear-resistant decorative laminate flooring materials, the decorative paper which exhibits the surface structure being at the same time coated with particulate corundum without the surface of the flooring materials thus produced showing any dulling.
The above-mentioned problem is solved by a method of impregnating paper used for the production of wear-resistant laminate flooring material comprising the steps of: a) taking paper; b) damping and impregnating said paper with an amino resin by the use of metering rollers; and c) additionally spraying onto said damped wet paper an additional layer of amino resin in a dispersion containing an abrasive substance and a flow-promoting agent; and wherein the final area density relative to the dry mass of raw paper amounts to 100% to 250%. As is preferred, the dispersion comprises 100 parts of the amino resin, 20 to 95 parts of the abrasive substance, 0.5 to 2.5 parts of a silane adhesion promoter, 5 to 25 parts of a flow-promoting agent, 0.1 to 0.4 parts of a wetting agent, 0.05 to 0.4 parts of a separating agent and of an amino resin hardener.
Further in accordance with the invention, a melamine resin is employed as the amino resin, and polyglycol ether, e-caprolactam or butane diol is employed as the flow-promoting agent, and the abrasive substance comprises at least one of aluminium oxide and silicon carbide having a mean particle size of 60 to 160 xcexc-m. In addition, a mixture of silicon carbide and aluminium oxide can be employed as the abrasive substance, and after the spraying step the impregnated paper can be pressed to form a panel.
One of the important differences of the process according to the invention lies in the fact that the mass or dispersion used for impregnating the decorative paper and for applying the wear-resistant bodies such as corundum particles is sprayed on or applied by the nozzle principle.
The nozzle principle has the advantage over application by rolling that the dispersion containing the wear-resistant bodies such as corundum particles is continuously and thoroughly stirred around before application and thereby is more or less uniformly moved. Accordingly appearances of deposits which lead) to a lack of uniformity are not observed. Therefore also one can dispense with the addition of viscosity-increasing materials or substances. On the contrary in fact one can introduce flow-promoting materials which achieve an improved distribution of the wear-resistant material such as corundum, which is of advantage in the press used for compressing the material.
A further advantage lies in the fact that one does not need to pay particular attention to using aluminium oxide of a particularly fine particle size, but that corundum or other particulate wear-resistant material having a significantly larger or coarser particle size can be employed. This has the further consequence that relatively small quantities of corundum or other particulate wear-resistant material are required in order to achieve high values of wear-resistance.
The consequence of these measures and advantages is that particularly transparent and brilliant surfaces of laminate flooring materials can be achieved according to the invention.
A further advantage of the invention lies in the fact that one does not, as in the known application of the mass or dispersion used for impregnation by means of spreading rollers, have to proceed with a relatively slow impregnation velocity of for example 18 to 25 m/min, in order to achieve an adequately uniform application, but that using the process according to the invention, in which the mass or dispersion is supplied by means of nozzles, one can achieve or realise impregnation velocities of 40 to 50 m/min.